Lasers may be used as components in transmitters for digital communications products. It may be useful for the laser to operate within as small an electrical power budget as possible, while providing sufficient optical power to span the communication link with low bit-error rate. The efficiency of the laser may therefore be important for the transmitter with respect to cost and/or power considerations. It is also useful for the laser to operate with a relatively high spectral purity, that is, with an output that is highly localized around one optical wavelength. This spectral purity may be desirable because emission at multiple optical wavelengths may introduce bit errors due to optical dispersion and/or wavelength-dependent modulation.